下列关于乙醇的说法中，不正确的是 [ ] A．乙醇是无色透明、有特殊香味的液体

如图中的装置MN可用来测量各种发动机的转速，在MN上在许多不同长度的钢片，从顺着钢片的刻度上读得固有频率为60HZ的钢片有显著的振幅，则可知发动机的转速是______r/min．

Why is（）fun What delights may its practitioner expect as his reward First is the sheer joy of making things. As the child delights in his mud pie, so the adult enjoys building things, especially things of his own design. Second is the pleasure of making things that are useful to other people. Third is the fascination of fashioning complex puzzle-like objects of interlocking moving parts and watching them work in subtle cycles, playing out the consequences of principles built in from the beginning. Fourth is the joy of always learning, which springs from the（）nature of the task. In one way or another the problem is ever new, and its solver learns something: sometimes （）, sometimes theoretical, and sometimes both. Finally, there is the delight of working in such a tractable medium. The（）, like the poet, works only slightly removed from pure thought-stuff. Few media of creation are so flexible, so easy to polish and rework, so readily capable of realizing grand conceptual structures. Yet the program（）, unlike the poet’s words, is real in the sense that it moves and works, producing visible outputs separate from the construct itself. It prints results, draws pictures, produces sounds, moves arms. Programming then is fun because it gratifies creative longings built deep within us and delights sensibilities we have in common with all men.

sometimes （）, sometimes theoretical, and sometimes both.

A．semantic

B．practical

C． lexical

D．syntactical

在计算一国国民生产总值的产出或“费用”计算方法中，使用了下列哪一种计算（）

A．消费+投资+政府购买+净出口。

B．消费+投资+政府购买-净出口。

C．消费+投资-政府购买+净出口。

D．消费-投资-政府购买-净出口。

以下关于我国领海无害通过制度的表述中错误的是：( )。

A．外国非军用船舶和航空器，享有依法无害通过我国领海的权利

B．外国军用船舶进入我国领海，必须经我国政府批准

C．外国潜水艇和其他潜水器通过我国领海，必须在海面航行，并展示其旗帜

D．外国核动力船舶和载运核物质、有毒物质或者其他危险物质的船舶通过我国领海，必须持有有关证书，并采取特别预防措施

正方形ABCD为侧垂面，对角线BD为侧平线，A在B的左上方，求该正方形的三面投影。